On the attribution of extreme weather events

"Finally, a comment on frequently asked questions of the sort: Was global warming the cause of the 2010 heat wave in Moscow, the 2003 heat wave in Europe, the all-time record high temperatures reached in many Asian nations in 2010, the incredible Pakistan flood in 2010? The standard scientist answer is 'you cannot blame a specific weather/climate event on global warming'. That answer, to the public, translates as 'no'.

"However, if the question were posed as 'would these events have occurred if atmospheric carbon dioxide had remained at its pre-industrial level of 280 ppm?', an appropriate answer in that case is 'almost certainly not'. That answer, to the public, translates as 'yes', i.e., humans probably bear a responsibility for the extreme event."

- James Hansen, "How Warm Was This Summer?" from NASA Goddard Institute for Space Studies.

The whole piece is worth reading, not least for the prediction that 2012 is "likely" to reach "record high global temperatures", after 2010 has already repeatedly broken the twelve month running average (temperatures in 2011 are likely to be slightly suppressed from record levels by the La Niña that has developed in recent months). I also talked about the difference between weather and climate back here.

Dr James Hansen is the head of NASA GISS and was the first academic to bring climate change into mainstream awareness at his US congressional testimony on 23rd June 1988, which became front page news when he claimed there was sufficient evidence to give 99% certainty that "It is already happening now".

As you may have noticed, Hansen takes his duties as a citizen (and grandfather), as well as a scientist, seriously. Last week Dr Hansen was arrested (once again) for civil disobedience while protesting coal mining through mountaintop removal, which manages to combine a whole raft of destructive effects on the way to disrupting the climate.

Here is another quote on attribution worth pondering:

"The point is that while it is a perfectly reasonable question to ask: “Was this event due to climate change?” it would more useful to ask a related question: “are we putting ourselves at greater risk of experiencing this kind of event?” And to that scientists can answer with high confidence: yes!

"Now, you might think this question is less interesting or useful, and perhaps not as worth asking than the first one. But we would argue that, in fact, it is very important to pose this question, and to carefully consider its answers.

"Think of smoking, sun bathing without sunscreen, eating lots of junk food and so on. You may not be able – ever – to unequivocally attribute one person’s problem to the effects of these activities: people develop lung cancer without smoking, for example, but as a population we know we are better off wearing sunscreen, watching our cholesterol, and not smoking, since all of these actions have been shown to make the chances of harm to our health lower."

- Nicole Heller, Claudia Tebaldi, and Phil Duffy, "Why Can’t Scientists Say the Recent Extreme Weather Events Are ‘Proof’ of Climate Change?" at Climate Central.

Chinese and US carbon emissions: myths and morality

Statistics and spin

"China is inappropriately made a scapegoat in this case because what causes the climate change is not today's emissions, it's today's atmospheric composition and we [USA] are primarily responsible for the excess carbon dioxide in the atmosphere - more than three times more than China and actually on a per capita basis more than an order of magnitude [i.e. ten times]. So to blame China and to say that we have to wait for them is nonsense."

- James Hansen, head of NASA Goddard Institute for Space Studies, in this interview.

Statistics can frequently be misleading. And so it really matters which statistics are given the most attention. It is true that China is currently the country that emits the most carbon dioxide each year. Yet Hansen is right to point out the massive historical and per capita disparity between the west and China (and India, of course). The climate change we are currently experiencing and the same again (more or less) already "in the pipeline" are due to emissions so far (there is a lag between the addition of greenhouse gases to the atmosphere and rising atmospheric temperatures as most of the energy initially goes into the oceans). And the carbon dioxide currently in the atmosphere is due very largely to the US, Germany and the UK (in that order).

Since cumulative emissions are more important than the current rate of emissions (due to the long period of time that about half the carbon dioxide we release stays in the atmosphere), then focussing simply on current rates without considering the cumulative totals obscures the bigger picture. And comparing countries with widely disparate populations also assumes that the only relevant moral unit is the nation state, a very odd assumption for individualists in the US to perpetuate. It makes much more sense to speak primarily in per capita terms. When these considerations are included, as Hansen points out, the US has little moral authority to consider China the largest contributor to the problem. Indeed, a further factor worth pondering is that roughly one-third of all China's emissions result from producing goods for western markets, so if we look at the consumption levels driving the dangerous emissions, then once again the west has little right to place the lion's share of blame for today's situation on China.

However, future emissions are also relevant, since (simplifying quite a bit), it is really the total amount of carbon dioxide humans release that matters. If we're to stay below 450 ppm (which has been the rough goal accepted by most governments - whether 450 is already too dangerous is a discussion for another day), then we've already spent more than half the carbon budget. Pre-industrial levels were around 280 ppm and we're currently at 390 ppm and rising (since more carbon dioxide is entering the atmosphere than leaving it). If this is accepted as a reasonable goal, then even if the US entirely stopped all carbon emissions tomorrow (impossible, but this is a thought experiment), China would never be able to emit as much carbon dioxide per capita as the US already has.

Does this mean that China (and other rapidly industrialising nations) bear no responsibility for their current (and rapidly rising) emissions? Of course not, but it is clear that the developed world has contributed far more to the problem than the developing world and so rightly ought to bear most responsibility for addressing it. Simply looking at current emissions obscures morally relevant considerations and enables the world's richer nations to downplay the role we have played in causing the mess. Unfortunately, such arguments are not widely understood or accepted in industrialised countries.

If you would like to see some of these statistics visualised, then Gapminder is an excellent resource. If you follow this link and click "play", you'll see a historical progression of various nations' contributions. The size of the circle indicates population size. The x-axis is per capita emissions and the y-axis is cumulative emissions. Colours are for region. You can play around with all the settings to see all kinds of relationships (a two minute tutorial is here). I haven't managed to find any graphs that compare per capita cumulative emissions. Doing so would demonstrate that China and the US are not simply in different ball parks but are playing entirely different games.

The problems with cap and trade

I mentioned back here that I'm not convinced that a cap and trade system will actually be effective in reducing atmospheric CO2e levels (which has to the point, doesn't it?). Here is a brief video giving some of the reasons to be hesistant about this proposal, which is at the heart of the upcoming negotiations in Copenhagen.

Indeed, James Hansen (the first climatologist to testify to US congressional committees and raise the profile of global warming back in 1988) is also opposed to cap and trade and thinks that it would actually be best for the upcoming negotiations in Copenhagen to collapse, since that would leave open the possibility of a more ambitious solution.

Many others who are critical of cap and trade nonetheless suggest that it is the best that it will be possible to do (politically) and so support the negotiations.

It is hard to know what to think about this. Politics is indeed the art of the possible and there is no point destroying an actually obtainable partial solution for the sake of a virtually impossible better solution. However, the questions are: (a) is cap and trade even a partial solution? (b) Will this partial solution still lead to catastrophe and so turn out to be no solution at all? (c) Are other suggestions really superior? (d) And are they truly impossible, or does their impossibility arise from a limited horizon of imagination sustained by powerful status quo interests?

To these questions, I do not currently have answers. But I am still yet to be persuaded that a revenue-neutral carbon tax (or rather, GHG tax) has flaws as serious as those associated with cap and trade.

UPDATE: An interesting opinion piece from James Hansen today critiquing cap and trade and proposing an alternative. And another leading climate scientist says the targets being offered by many of the major players are "token gestures".

UPDATE #2: Now I have finally seen a coherent argument against a carbon tax. It can be found here, although the focus of the piece is a critique of one particular proposal that is aimed at delay. In short, Hamilton argues that cap and trade (for all its faults) is the horse that has already run half the race and we don't have time to go back to the start again.